This invention relates to a method and apparatus for measuring and displaying in numerical form the speed of a moving member. In high speed document sorters or similar devices wherein documents are transported at high speeds past a reading member such as a magnetic transducer and where data is read from each document for use in sorting the document, it is desirable to know the speed of the document to insure that the document will move past the reading member at a speed which will allow the reading member to provide a valid read operation. Normally the velocity of the document must fall within a predetermined range of velocity values in order that the reading member will produce a valid read operation. One method of measuring the speed of a document over a given distance is to set up two photo-sensors at a fixed distance (d) apart adjacent the path of movement of the document. When the object is sensed by the first sensor a digital oscillator is started and when the object reaches the second sensor the oscillator is stopped. The number of pulses (n) produced by the oscillator during this time is counted. The time taken for the object to travel the fixed distance between the two sensors is given by the equation: EQU t = n .times.(1/f )
where f = frequency of the oscillator. Since the fixed distance (d) between the two sensors is known, the speed (v) of the document is given by the equation EQU v = (d/n) .times. f.
To obtain a high accuracy of measurement in measuring the time (t), the oscillator frequency must be made very large and therefore the number of pulses measured must be very large. In utilizing digital processing equipment to determine this speed, a large memory would be required to store the number of pulses in addition to requiring a large capacity for performing the division of df/n digitally, the operation being relatively slow due to the number of divisional operations required. It is therefore an object of this invention to provide a method and apparatus for measuring the speed of a document utilizing digital apparatus. It is another object of this invention to provide a method and apparatus for measuring the speed of a document wherein digital multiplication rather than digital division circuitry is utilized. It is a further object of this invention to provide a method and apparatus for measuring the speed of a document which requires minimum system hardware to implement the method resulting in lower cost of operation.